Resistance element and process of making same.



1 Q 6 CROSS REFEKZIIJE EXAMINER 3. H. READ. -RESISTANGE BLBMENTA'ND PR 001388 OF MAKING SAME.-

APPLIOATIQN FILED JUNE 5, 1914.

- Patented Feb.2, 1915.

lumwzloz fizzy/AM Witueoou R. H. HEAD.

RESISTANCE ELEMENT AND I'hOGESS OF MAKING {SAME APPLICATION l'lbfll.) JUNE 5,1914.

Patented Feb. 2, 1915.

2 SHEETS-SHEET 2.

Ql m I w wunema UNITED STATES- PATENT OFFICE.

ROBERT E. READ, OF WA SHINGTON, DISTRICT OF. COLUMBIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

RESISTANCE ELEMENT AND PROCESS OF MAKING SAME.

T all whom it may concern:

Be it known that I, ROBERT H. READ, a citizen of the United States, residing at \Vashingion, in the District of Columbia, have invented new and useful Improvements in Resistance Elements and Processes of Maliing Same, of which the following is a specification.

This invention relates to resistance elements for electric heaters or rheostats or the like, the object being to produce an element that will have a large radiating or heat transmitting surtaee ermitting a higher current density in t e conductor than usual and therefore admitting ofa more rapid communication of heatto. thetranslating apparatus to which it; is applie I havefheretofore described in prior applications devices of this general character.

based on the idea of tion.

The present invention permits a cheaper construction to be employedby using asbestos insulation. Asbestos is not. so perfect an insulator as some mineral oxids, but with a moderate insulation depth is practical for use with commercial incandescent lighting I voltages, and admits of cheap and ready covering of the core wire with a solid, symmetrical insulating spacer.

The invention also includes a cheap and effective type of terminal adapted to lead current from a sup ,ly circuit to the heating wire in a way w ich will be durable and will prevent damage to the element through the connections with the supply circuit.

In carrying out my invention I cover a resistance wire with asbestos by Winding a pure asbestos cord circumferentially around the wire, by-coverin it with a tape of asbestos, by surroun ing' it with asbestos flock, or by inclosing it within an asbestos tube. I then inclose the insulated wire in a malleable metal tube, preferably a seamless metal tube, and the whole is drawn,

firmly compacted on the resistance wire. .The ends of the resistance wire before or after the asbestos.

covering is applied -are slipped into a copper tube and united thereto by brazing, or

Specification of Letters Patent.

a metal sheath sepa rated. from a core wire by powder insulaby shrinking the copper on the wire and preferably also reducing the cross-section of both the core wire and copper tube where the joint is made, or by suitably indenting the oint to efi'ect a local mechanical interlock between the core and the terminal. Thus the joint is made strong and will not Patented Feb. 2, 1915. Application, filed June 5, 1914. Serial No. 853,286.

become detached in service, and a good and I eflicient heat relation is maintained keeping f e the joint between the highly conductive copper terminal and the high resistance core cool because of the asbestos and surrounding seamless metal covering of large heat radiating surface. Moreover, the outer covering being watertight prevents entrance of: water and moist a1r.

tion therefore comprises anasbestos covered resistance wire inclosed in a seamless metallic armor or sheath. It comprises other more specific features, as well as a process 'of making the insulated wire.

' In the accompanying drawings illustrating my invention, Figure 1 enlarged a resistance wire with tubular terminals of good conducting material secured; thereto. Fig. 2 is a similar view of a wire with terminals secured by reducing the cross-section at the joint. Fig. 3 is a similar. view showing an alternative type of joint. by which the wire and terminals are secured together. Fig. 4 shows enlarged a woven or raided asbestos tube adapted to be braideda around the wire or slipped over it before or after the terminals are applied. Fig. 5 is a sectional view of the asbestos covering shown in Fig. 4. Fig. 6 shows an, apparatus for inclosing a resistance wire within a metal sheath with an intervening layer of asbestos. Fig. 7 shows a mode of covering a wire'with asbestos cord. Fig. 8, shows a seamless metal tube adapted to be slipped over an asbestos insulated wire and afterward to be shrunk upon it. Figs. 9 and 10 show in plan and section a metal strip covered with asbestos flock cemented fast and adapted to be folded or curled about a resistance wire as in Fig. 6. 'Figxflshews the form of 'oint of Fig. 2, the parts being much magni ed. Fig. 12 is a magnified viewin section of an asbestos covered wire with aseamless sheath. Fig. 13 is a similar view with an additional curled sheath inside the seamless sheath.

shows much My invenmanna-hm-..

Asbestos has been employed to a considerable extent for insulating wire but is usually held together and to the wire by organic binders such as glue and frequently contains a large proportion of cotton. Such materials do not withstand heat and on considerable rise of temperature char and produce short-circuits with great damage to the translating device. With pure asbestos or such as contains a very low percentage of organic material a resistance device may be run hot without damage and may be applied to commercial incandescent lighting circuits of 120 volts when the insulation is of suflicient depth to withstand leakage. It has the merit of permitting an annular bed of insulation to be readily formed about the wire and being a compressible solid is maintained central when subjected to the reducing action of diesor rolls. .-If the material is applied dry it makes a stable insulation, and when firmly compressed becomes an effective heat transmitter to con- "ey the heat of the wire to a translating dey vice.

Referring now to the drawings the core wire 1 is of any suitable high resistance metal or alloy. German silver, nickel-steel, nickel-chromium, nickel-manganese or the like may be employed of which there are many kinds on the market. A wire of the proper section may be selected and of a' length to permit the desired current to be transmitted. To the ends either before the asbestos is applied or afterward I secure terminals. I prefer to form the terminals of copper tubing drawn to a size to receive the resistance wire as shown at 23 in Figs. 1 to 8. They may be secured in several different ways, by soldering, brazing, swaging, rolling or otherwise shrinking the parts together. In Fig. 1 the terminal tube is shown as brazed or soldered to the resistance wire. In Fig. 2 the terminal tube is slipped over the ends of the resistance wire and the crosssection of the joint at a point within the terminus of the wire, as at 4, is reduced.

This may be effected in several ways, by-

placing the joint between the hammers of a swaging machine, by placing between rolls and rocking the rolls, by compression in a divided die, or otherwise. In Fig. 3 the tubular terminals are secured by indenting the sheath on an anvil to cause the copper tube and wire to metallicallyinterlock, as at 5. A lead wire may be locked in the end of the copper tube as indicated in Figs. 1 and 2 or the tube may be reduced in section to a solid wire.

The resistance wire may be inclosed in a woven asbestos tube 6, Figs. 4 and 5. If applied before the terminals are secured the tube is slipped back on the wire when the joint with the copper tube is made. When an asbestos winding is applied to the resistance wire, it is more convenient to wind Fig 8 is then slipped over the covered wire and the whole drawn, rolled or swaged down in cross-section until the asbestos is firmly compacted on the resistance wire. A section of the sheath is cut off at each end of the element and the cord unwound. A tubular copper wire is then slippedpver the bared resistance wire and secured in one of the ways shown on Figs. 1 to 3. The cord is then wound over the joint and a piece of copper tubing slipped over the winding and sheath ends and soldered or brazed on the ends of the sheath and is then reduced as at 4-4, Fig. 11. The ends where the copper lead wire projects or protrudes from the seamless sheath may be sealed with a cement of ground flint and silicate of soda and hardened by heat which will preserve the insulation moisture proof.

In Fig. 6 is shown a mode of covering the.

core wire. The wire is shown at 1 and is led from a spool under tension through a centering die 9; the latter has a flaring mouth and a cylindrical bore 10. A metal tape 11, is led, under tension from a reel 12 through guides 13 at each side of the ta e which lea it true to the die opening. 11 top of the metal tape or ribbon is carried an asbestos tape 11 preferably cut-or woven on the bias, which may be fed by hand or from a reel. In starting the metal ribbon is sheared to a taper as at 15, Fig. 9 by.

which it may be drawn through the die. As it passes through the die the metal ribbon 11 is folded around the asbestos tape which latter will inclose the resistance wire. A steel blade 15 guides the curled tube and keeps the seam straight. The inclosed wire is then reduced in section until the asbestos is firmly compacted onthe resistance wire. A seamless metal tube 7, Fig. 8 is then slipped over the metal covered wire and shrunk into intimate engagement by rolls, dies or a swaging machine. A short section of the double sheath is then removed at each end by a revolving knife such as a small pipe cutter exposing the asbestos. The asbestos is folded back and the tubular co per terminals applied and secured as already described. The asbestos may be folded around the jointor if it has been damaged in removing the sheath 9. piece of asbestos tubing may be placed .over the joint. A short piece of seamless metal tubing is then pushed over the sheath and brazed or soldered. The cross-section is then reduced as at 4,'Fig. 11, thus locking the core to the sheath, and the core to the terminal.

In place of the metal'tape 11 and asbestos ribbon 14 I may cement to the face of the metal by silicate of soda a layer of asbestos flock, as shown in Figs. 9 and 10 and then the flock covered metal tape may be curled in the die of Fig. 6 around the re stance -wire with the flock next the wire; after points where a mechanical {interlock be tween the core and terminal is produced,"the core remains constant in resistance, and the proper length for a required service may be accurately predetermined for a resistance wire of specified specific resistance. The resistance wire is led from a spool 6 under tension and through a winding machine carrying a slidable bobbin of asbestos cord, 17. The cord is threaded through eyes 18 carried by the revolving support for the bobbin and is preferably served in two superposed layers. The wire is guided loosely through a stationary tube 19 and may be smoothed down by a pair of rolls 20. When wound the desired length the wire may be cut ofi and terminals applied, and a metal sheath shrunk over the asbestos in the way already described.

I do not claim in this application a corewire of high resistance in a seamless tube with a closely compacted owder insulation, such matter being claimed in my copending application #841,544, filed May 28, 1914, nor do I claim inclosing a wire with powder insulation in a folded metal sheath, which is claimed in my application #572,778, filed July 19, 1910.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is 1. A resistance element for electric heaters or the like comprising a high resistance core wire, a bed of asbestos surrounding the same, and a seamless metallic sheath tightly embracing the asbestos, the core wire projecting through the seamless :sheath, the

protruding part being of higher conductivity than the core wire.

2. A resistance element for electric heaters or the like comprising a high resistance core wire, a continuous length of asbestos surrounding the wire in an annular bed, and a seamless metal tube tightly embracing the asbestos, the core wire having terminals projecting from the tube ends of higher conductivity than the core wire.

3. An insulated wire adapted to withstand heat consisting of a core wire, a surtos, a metallic sheath tightly embracing the asbestos, and a terminal of higher conductivity than the core metallically interlock- .ing therewith, and surrounded by heat rakliating means to cool the joint.

5. A resistance element for electric heaters or the like comprising a core wire-of high resistance, a surrounding layer of asbestos, a good conducting terminal connected to the core wire, and a metallic extension of the sheath housing the joint insulated from the core wire but in good thermal relation thereto.

6. A resistance element for electric heaters or the like comprising a high resistance core wire, a surrounding layer of fireproof insulation; a malleable sheath inclosing the insulation, good conducting terminals con nected to the core wire by a tubular joint, and means for keeping the joint cool.

7. A resistance element for electric heaters or the like comprising a high resistance wire, a surrounding layer of fireproof insulation, a malleable sheath tightly embracing the insulation, low resistance terminals for the wire mechanically interlocking therewith to prevent accidental separation, the sheath covering the interlocking region or zone.

8. A resistance element for electric heaters or the like comprising a high resistance core, a surrounding closely compacted bed.

of fireproof insulation, a water tight metallic sheath inclosing the insulation, terminals projecting from the ends of the sheath, and a moisture proof seal at the ends of the sheath.

9. A resistance element for electric heaters or the like comprising a high resistance core, a tightly -compressed bedof asbestos cord wound on the same, a watertight metallic sheath around the asbestos, and projecting terminals of good conductivity joined to the core within the sheath.

10. The process of making a resistance element consisting in inclosin a high resistance vwire circumferentia y wlth a spirally WOllIld strip of asbestos, surrounding the asbestos with a metallic sheath, and reducing the cross-section of the sheath until the asbestos is firmly compacted around the wire. 11. The process of making a high resistance sheathed wire consisting in covering a core-wire with asbestos insulation, applying a tube of highly'conductive metal over the ends, thereby forming terminal joints,

and shrinking a watertight metal cover on the asbestos, the ends of the cover overlap )in" the terminal oints. l a

12. The process of making a high resistance element consisting in sun-minding a; high resistance wire with asbestos, 1nclos1ng it within a seamless metal tube, applying tubular copper terminals to the ends of the wire, and reducing the section of the joint to mechanically lock the terminal to the wire.

13. The process-ofl making a resistance ROBERT H. READ.

\Vitnesses CHAS. E. BROOK, E. B. MCBATH.

low resistance terminals for the wire ends. 20 

